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    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <script>
        // country='中国' 这就是参数默认值  
        function  selfIntro(name,age,country='中国'){
            console.log('我叫'+name+'今年'+age+'岁来自'+country);
        }

        selfIntro('张三',18);
        selfIntro('拜登',85,'漂亮国');

        


    </script>
</body>
</html>